The diaphragm of a pressure transducer is its most crucial part and yet is exposed to the most arduous conditions. Pressure transducers are employed for measuring pressure changes in internal combustion engines, turbines, hydraulic and ballistic systems, rockets, explosive forming machines etc. Gaseous or liquid media, with their frequently changing temperature and pressure, act on the diaphragm, which has to transmit the resulting force onto a mechano-electric transducer element. This element may be piezoelectric, inductive, resistive, piezoresistive, or capacitive in its action. This element is then linked by a cable to electronic amplifiers or bridges, whose output signals are supplied into cathode-ray oscillographs, magnetic tape recorders or electronic recorders.
Because the diaphragm is often exposed simultaneously to rapid temperature and pressure shocks, under continuous operation it must withstand very severe mechanical stressing. In addition, highly corrosive gases are present due to the sulphur content of fuels. In a typical design, the diaphragm is welded to the supporting surface on the body of the transducer, but this has the further disadvantage that the weld is close to the parts of the diaphragm which have to sustain the severest stresses. As a result, fatigue fractures occur, especially in the immediate proximity of the welds, assisted in part by recrystallization process. Temperature shocks, such as those imposed by the propagation of the flame front in internal combustion engines, cause internal thermal expansion, which lead to spurious signals that are superimposed upon the pressure signal. The design of the diaphragm part of such pressure transducers therefore involves a number of requirements which are difficult to reconcile, and this is one reason why the solutions achieved up to now have been less than satisfactory.